Free cutting alloys



Patented Jan. 7, 1936 FREE CUTTING ALLOYS William L. Fink, Oakmont, Pa., assignor to Aluminum Company of America, Pittsburgh, Pa., a

corporation of Pennsylvania,

No Drawing.

2 Claims.

The invention relates to aluminum-copper alloys and is particularly concerned with alloys of this nature containing substantial amounts of cadmium.

5 Despite the manifold advantages connected with the use of aluminum and its alloys in commercial fields, there is an inherent drawback which somewhat curtails their use in certain potential applications. Aluminum alloys, for instance, containing from about 4 per cent to about 12 per cent of copper have a. wide range of use- 1 fulness on-account of their favorable mechanical properties in the cast or wrought condition and their susceptibility to improvement or varia- 15 tion of physical properties by suitable thermal treatments. Thesealloys, within various composition ranges, may be rolled, drawn, forged, ex-

truded, or otherwise mechanically deformed. The grain is thereby refined and the physical properties considerably improved. The inherent disadvantage hereinabove mentioned consists in the fact that machining operations such as boring, drilling, shaping, planing, or lathe-cutting aremost successfully carried out only by using certain precautions which increase the expense of the operation and which occasionally force the substitution of another alloy more readily machinable but otherwise not so desirable from-the standpoint of physical properties. When alloys are diflicult to machine this disadvantage becomes evident in many cases through rapid wear of thezcutting tool edge which necessitates frequent resharpening. In such cases where machining is difiicult continual lubrication is required, the machined surface is rough and irregular and the chip has a tendency to form long curls or spirals that may foul the tool or operating parts of the machine. The need is thus immediately apparent for an alloyof good working characteristics and satisfactory physical properties yet possessing favorable machining qualities so that articles of good surface appearance-may be formed .therefrom economically and successfully. An alloy satisfying these requirements may, for convenience, be styled "free machining or "free cutting and alloying constituents added to accomplish the desired results may be termed I free machining constituen Accordingly an object of this invention is the production of an aluminum base alloy containing from about 4 per cent to about 12 per cent of copper which exhibits free cutting characteristics. A further object is the production of such an alloy which possesses physical properties equal Application September 18, 1933, Serial No. 689,892

to or superior to those of the ordinary aluminumcopper alloys of the .prior art.

My invention resides in the discovery that these objects are accomplished by the addition of from about 0.05 per 'centto about 1.5 per cent of cad- 5 mium to aluminum base alloys containing from about 4 per cent to about 12 per cent of copper. Aluminum-copper alloys containing as much as 5 or 6 per cent of copper may be readily rolled or forged. Considerably more than this amount of copper maybe added while the alloys still remain amenable to extrusion processes. Aluminum base alloys containing from about 4 per centto about 12 per cent of copper may be readilycast in sand or permanent molds. In the lower copper range such alloys are used, for instance, as screwmachine products such as bolts, nuts, and screws, while automotive parts such as crankcases or pistons, may be cited as applications of the casting art in the higher copper range. Both of these adaptations, and more especially the screw-machine products require a high degree of machinability for economical commercial production. Such applicationshave heretofore been attended by the difficulties and disadvantages hereinabove 25 set forth as consequent upon inferior machining characteristics. By preparing alloys in accordance with my invention the aluminum-copper type of alloy is rendered considerably more amen- 30 able to machining operations. The chips flow more freely from the article being cut, they are more breakable, and are less objectionable in nature than chips from the same alloy containing no cadmium. The machining operations can also be performed more rapidly and economically, and the machined surface presents a bright, smooth,

pleasing appearance.

The addition of cadmium not only improves the machining quality of the alloys herein dis- 40 closed but it favorably affects the tensile strength as well. In the heat treated and aged condition cadmium in amounts between 0.05 and 1.5 per cent efiects an increase in the yield point, ten- 45 sile strength, shear strength, and Brinell hardness of aluminum-copperalloys containing between about 4 per cent and 12 per cent of copper, the elongation dropping off. appreciably. Such an increase in strength and hardness is naturally dependent upon the quantity of cadmium present in the alloy." It thus becomes possible to accommodate the aluminum-copper alloys to 'varying situations and needs by a proper choice of the amount ofcadmium while ,55

retaining the advantage of machining characteristics.-

Within the composition range hereinbefore disclosed I have found that the following alloy embodies preferred characteristics: An alloy of 6 per cent copper, 1.0 per centcadmium, balance substantially aluminum. As a general rule the amount 'of free machining constituent may be reduced as the copper content is increased.

The cadmium may be added most conveniently by dropping it in solid metallic form into a molten heat of aluminum-copper alloy. The melting point of cadmium is considerably below that of aluminum-copper alloys, so that it becomes molten almost immediately. The temperature of the molten alloy should not exceed an improvement in 1400 F. in order to avoid excessive volatilization of cadmium. A thorough stirring insures a good alloy mixture.

The alloys within the scope of this invention are amenable to the usual thermaltreatments suited to aluminum-copper alloys, and now familiar to the art.

The term aluminum-copper alloy as used herein and in the appended claims embraces those aluminum alloys containing more than 50 per cent aluminum associated with copper in the proportions defined here'inabove as well as the customary impurities found in aluminum ingot of commercial grade or picked up in the usual handling operations incident to ordinary melt- 10 ing practice.

I claim:

1. An aluminum-copper alloy containing from about 5 per cent to about 12 per cent of copper and between about 0.05 per cent and 1.5 per cent 15 of cadmium, the balance being aluminum.

2. An aluminum-copper alloy containing about 6 per cent of copper and about 1 per cent of cadmium, the balance of the alloy being aluminum.

WILLIAM L. FINK. I 

